1. Field of the Invention
This invention relates generally to methods and apparatuses for demounting workpieces from adhesive film and, in particular, for demounting semiconductor wafer-fabricated chips or dies such as circuit chips, laser chips, and laser bars from adhesive film, after separation operations such as dicing, sawing, or scribing and breaking, without damaging the workpieces.
2. Description of the Related Art
The following descriptions and examples are not admitted to be prior art by virtue of their inclusion within this section.
The manufacture of miniature semiconductor, optoelectronic, and other electronic devices typically involves forming a number of devices on a semiconductor wafer. The semiconductor wafers are typically 2 to 8xe2x80x3in diameter and approximately 0.010xe2x80x3to 0.020xe2x80x3thick. The wafer contains a grid, array, or other layout of devices, which are to be separated into discrete chips or dies. These devices can include integrated circuits such as microprocessors or other circuits consisting of networks of smaller devices such as resistors, transistors, diodes and other electrical circuit elements; or optoelectronic devices, such as semiconductor lasers or photodetectors. Electronic and IC semiconductor chips are typically flat and rectangular (typically square), ranging from about 1 mm to about 10 mm square and from about 0.4 mm to about 0.8 mm in thickness. Optoelectronic devices, such as laser chips, may be less than 0.25 mn along a side (width) and less than about 0.1 mm in thickness (height). Bare die are very fragile and some, such as laser chips, are also very brittle. Laser chips may include long, fragile laser bars, each of which may be separated into a number of edge-emitting lasers at a later stage of processing. Laser bars, for example, may be about 15 mm long, with a rectangular cross-section (about 0.3 mm wide and 0.1 mm in height). These various objects, devices, die, dice, articles, and IC chips may be referred to herein generally as workpieces.
In order to perform various processing tasks on the wafer, such as dicing, scribing and breaking, or sawing the wafer to separate the individual workpieces, the wafer is often mounted on an adhesive film, sometimes referred to as wafer handling tape or film, sticky sheet, polymer support film, adhesive web, wafer tape, tacky tape-adhesive tape, and the like, and generally referred to herein as adhesive film. Adhesive film comprises a carrier layer or carrier film coated on one side with adhesive. Mounting the wafer to adhesive film helps to hold the wafer in place during the dicing operation and to hold the separated workpieces (chips) in place after dicing is complete.
The adhesive film can be affixed to a film support frame, such as an annular retaining ring hoop frame, either by hand or with a wafer film frame mounting device. The support frame may be mounted in an expanding device to expand (stretch) the adhesive film, before the wafer is mounted to the adhesive film and/or after the wafer is diced into discrete workpieces. During and after processing (such as dicing, sawing, scribing and breaking, fracturing, expanding, and the like), tension is maintained on the adhesive film with the annular retainer ring. The support (e.g., hoop) frame may comprise, e.g., concentric inner and outer hoops, which are clamped to the adhesive film. A hoop frame may consist of stainless steel, plastic, or other suitably strong and rigid material. The hoop frame may have a diameter from 5 to 8xe2x80x3, for example, so that the size of the supported adhesive film surface is sufficient to mount a wafer. The hoop frame and adhesive film together provide a wafer frame onto which a wafer may be mounted.
After separation of the workpieces from each other, the workpieces need to be removed from the adhesive film without damage to the workpieces. For laser bar workpieces, a wafer expanding device is often used to separate the workpieces further from each other. After separation and expansion, there may be, for example, 30 to 40 laser bars mounted to a given piece of adhesive film, separated from each other by about 0.1 to 0.2 mm. The workpieces are then manually removed from the expanded film through the use of tweezers, vacuum pencils, vacuum collets, or vacuum tips, sometimes in combination with ejector needles, pistons, probes, or protruding bumps or rollers, or through the use of devices such as de-mounters, automatic pick and place machines, and die ejector systems. For example, with a pick and place system, a video screen allows an operator to position the pick up collet over the center of the die, and one or more needles pushes up from the back and dislodges the die from the adhesive film. The vacuum collet then lifts the die from the adhesive film and places it into the carrier (such as a waffle pack or gel pack).
However, because the workpieces are so small and fragile, the manual contact between the workpieces and devices such as tweezers, ejector needles, pins, and rollers can damage the workpieces, e.g. by forming micro-cracks in the device or even breaking the device into separate pieces. This is especially the case with long, thin objects such as laser bars. Thus, it can be time-consuming and difficult to remove such workpieces from adhesive film without damage.
Accordingly, there is a need for improved methods and apparatuses for demounting workpieces from adhesive film and, in particular, for demounting semiconductor wafer-fabricated chips or dies such as circuit chips, laser chips, and laser bars from adhesive film, after separation operations such as dicing, sawing, or scribing and breaking, without damaging the workpieces.